In nuclear medicine diagnostic imaging a radionuclide is administered to a patient and a nuclear camera or gamma camera such as the Anger gamma camera shown in U.S. Pat. No. 3,011,057 is used to produce a visual image of the distribution of the radionuclide within the patient. The nuclear or gamma camera devices that detect the emitted radiation are used in conjunction with a collimator to selectively filter the passage of emitted radiation from the patient to the gamma camera. The gamma camera includes a scintillation crystal positioned behind the collimator. The crystal when struck by radiation scintillates or emits visible light. The visible light is detetected by transducers such as photomultipliers and translated into electrical signals.
When gamma cameras were first used for medical diagnostic imaging, they produced images of organs such as the brain and thyroid gland. Through the years there has been significant improvements in the cameras and new radioactive isotopes for ingestion by the patient have been developed. The improved cameras along with the new radioactive isotopes have been used for conducting whole body studies to detect cancer in the patient in such places as in the bone marrow. More recently, the gamma camera systems have been used to obtain tomographic images in studies known as emission computed tomography (ECT) or single photon emission computed tomography (SPECT).
These gamma camera systems are used to cause the gamma camera detector means to orbit the patient and acquire data during orbit. The data is then used with reconstruction algorithms to provide tomographic images of the portions of the patient orbitted.
The equipment for enabling the scintillation detector to orbit the patient comprise a stationary gantry having a rotor supporting the nuclear camera detector means during the rotation of the nuclear camera detector means about the patient. Originally, the detector means was rotated in a circular path. However, soon it became apparent that images with a greater resolution could be obtained if the path was modified so that the gamma camera was proximate to the patient during the entire orbit. Thus, the nuclear camera detector means and the rotating portion of the gantry were programmed and controlled to follow complicated orbital paths. A further improvement in the ECT systems comprised using more than one head; i.e., more than one nuclear camera detector on the rotating part of the gantry.
Up until now the rotatable nuclear gamma detector means was electrically coupled to the stationary portion of the ECT system by cable arrangements. For example, power for the special photomultiplier tube power supply is required. The special power supply was either mounted on the stationary portion of the gantry or on the rotating portion. In either case, power had to be supplied to the rotating portion of the gantry for among other things, powering the photomultipliers. Conventionally, the required power is transmitted to the rotating member via flexible power cables. Complicated cable arrangements are provided that enable sufficient play in the cables so that the rotating portion of the gantry can complete at least one rotation.
In addition to the power supplied to the rotating portion of the gantry, it is also necessary to supply control signals to the rotating portion of the gantry. The control signals are used in the control of such things as the locus of the path taken by the nuclear gamma camera detector means during its rotation about the patient.
Also, the data; i.e., the electrical signals provided by the photomultiplier tubes, for example, have to be supplied from the rotating portion of the gantry to the processing means which is removed, from the gantry.
In practice the cabling arrangements for transferring power, control signals and data to and from the rotating camera head are a constant source of maintenance problems. In addition, the cabling severely limits the rotation. Thus, in practice the gamma camera head can only be rotated through approximately one or two rotations. This limitation slows down the examinations significantly.
In addition, with the use of faster radionuclides the capability of rotating more than once is even more desirable. For example, normally the rotating head is brought through one rotation in a slow mode to assure that there is no interference problems between the rotating portions of the gantry and stationary portions of the system including the patient bed. With the present equipment it is necessary to return the rotor to the beginning of its rotation after the slow trial run by reversing the rotation step and then to once again rotate through the data acquisition arc while acquiring data. The necessity of reversing the rotation requires extra time. It would be much more efficient if it was possible to continue the rotation and acquire data rather than having to reverse the rotation to return to the starting position.
Another advantage is that the continuous rotation capability makes it possible to use multiple rotations with each rotation at a higher speed than presently used during acquisition whereby even though less data is acquired per rotation the plurality of rotations results in more data being acquired such that true motion correction in .real time can be obtained by the multiple rotation enabling multiple views from the same angular position. This makes it possible to accurately determine motion and, for example, to reject the data from one revolution out of many. It also enables averaging of the data and thus improves the signal-to-noise ratio and the uniformity of the slices. In the prior art "nearby" views were used in the motion correction algorithm, and true motion correction was not possible. With multiple rotations true motion correction even in real time is now possible.
A related feature of the inventive capability of performing repeated revolutions about the patient is the capability of more absolutely determining patient motion and of rejecting data obtained during a revolution when the patient motion was excessive.
Since faster and repeated revolutions about the patient are used during acquisition cycles, the necessity of half life time corrections for such isotopes as .sup.13 I, 99mTc and 20T are not needed. A related feature is that ultra short life isotopes which were previously not feasible for use are now useable.
Yet another feature of the present invention is the capability of performing whole body scans by having the camera head or heads follow a cylindrical helical locus about the patient by combining elliptical and longitudinal motions.
Yet another related feature of the present invention provides for an evolving image. The camera head or heads continuously revolve about the image, with each revolution requiring about 30 seconds. Image reconstruction starts shortly after the first half of the first revolution. The image evolves as the number of revolutions increases. The operator stops the acquisition when he is satisfied with the quality of the evolved image.